Impacts of thermal aging and water absorption on the surface electrical and chemical properties of cycloaliphatic epoxy resin

New techniques for measuring surface degradation are applied to the study of surface tracking resistance of materials intended for outdoor use. Cycloaliphatic epoxy resin (CAE) with 200 pph silica powder was aged under accelerated conditions for 100 h (100 to 250°C) and then its tracking resistance was assessed. The tracking resistance of CAE that was exposed to water absorption (0 to 3.3%) also is evaluated. Changes on the surface layer (1 to 10 μm) with thermal treatment are revealed by employing scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analysis, attenuated total reflection (ATR)-Fourier transform infrared (FTIR), reflective visible spectroscopy and thermal gravimetry (TG)-differential thermal analysis (DTA) mass spectrometry (MS). The tracking resistance of CAE aged above 170°C is particularly reduced. Surface resistivity declines with rising temperature of thermal aging. The lowering of surface resistivity enlarges the leakage current passing at the aged surface layer and increases the surface temperature of CAE. This would accelerate thermal aging. It also is shown that absorbed water in CAE decreases tracking resistance. The effect of absorbed water during the initial stage of a tracking test is described. Under saline pollution and moisture, thermal aging affects not only surface tracking but also electrochemical erosion derived from sodium hydroxide which forms through electrolysis of sodium chloride. Electrochemical erosion enhances water uptake for CAE, which can lead to tracking resulting from absorbed water